= Solution
Weather-forecast errors arise from uncertainty in the initial atmospheric state, including <Measurement error>[measurement noise], incomplete spatial coverage and imperfect <data assimilation>; from model error, including unresolved <Cloud>[clouds], <convection> and turbulence, approximate physical parameterizations and imperfect boundary forcing; and from <discretization>, <Numerical integration>[time stepping] and <Rounding error>[roundoff]. <Sensitive dependence on initial conditions> amplifies suitable small errors through nonlinear dynamics, limiting deterministic predictability even with a good model. It is an amplification mechanism rather than a separate observational noise source. <Ensemble forecasting>[Ensemble forecasts] sample some initial-state and model uncertainty, but their spread need not represent every systematic error.
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